The present invention relates to an A.C. Power Supply Circuit having means for preventing a surge of current caused immediately after turning on a power supply, having an inductive load including a magnetic core device, such as a high-voltage transformer.
A power supply used for a high power radio comminication transmitter is normally controlled so that it may be switched on after a receiver and the like have been turned on. The power supply control for the transmitter is achieved by controlling the input of the power supply transformer. Since the power supply transformer is inductive, an excessive current surge is caused when turned on. Recently developed completely transistorized transmitters can suffer component damage by the current surge.
A conventional A.C. Power Supply Circuit, which is adapted to prevent the current surge, has a switching circuit having a so-called "soft-start means" which prevents the current surge by successively raising the voltage applied to the load. The switching circuit provides control over resistors or reactors inserted in series with the load by successively short-circuiting them. Alternatively, if a thyristor is employed, its conducting phase angle is successively increased. As an example of the latter method, reference is made to an article by K. Kishi at al entitled "Thyristorized Constant-Voltage D-C Power Supply for High-Power Transmitter" published in "Toshiba Review (Vol. 25, no. 12, p.p. 1545-1550). As an example of the former method, reference is made to the instruction manual for Power Supply Model 1029, 1031, and 1032 published by Enengy Systems, Inc., Palo Alto, Calif., U.S.A.
It is difficult, however, for these conventional power supply circuits to keep the current surge lower than 1.5 times as large as the nominal current. Usually these conventional techniques involve a large number of resistors or reactors for the successive short-circuiting or a very slow time-consuming increase in the conducting phase angle of a thyristor.